Mold making is a wide-ranging art form which invokes varied materials as well as techniques. The choice of mold making procedure depends as much on the model as the skill and dexterity of the mold maker. So is the case for the mold making materials.
The simplest form of mold is a block mold where you simply pour the mold making material over the object or statue to be replicated. Intricate shapes may require the mold to be made in two or even more parts. More complex techniques range from blanket molds and glove molds to injection molds and more.
And once the mold is ready, the artist moves on to making the final cast from the mold. Again, the choice of the techniques and materials varies from artist to artist and application to application.
A lesser known technique of making casts is the slush casting. This is a traditional method of permanent mold casting wherein the liquid casting material is not allowed to completely solidify in the mold. Once the desired thickness is obtained, the remaining material is simply poured out.
This technique comes in handy for casting hollow items such as toys, decorative pieces, statues, ornaments, components, etc.
The procedure is pretty simple in fact. The mold is placed on a flat surface so that the opening is on the top. The casting material is slowly poured into the mold opening. This could be clay slip, liquid latex rubber, molten metal (usually zinc, tin or aluminum) or even something else. The mold should be rotated a bit so that the material swirls around and completely coats the sides and bottom.
Once the material starts cooling or setting in the mold, it is turned over and the remaining material is poured out of the mold. A thin skin is left behind and this will solidify to form the hollow cast.
To form a thicker shell, the casting material simply needs to be left in the mold for a longer period. Alternatively, if the cast seems to be too thin, the pouring in and out process is repeated until the desired thickness is built up.
The cast is then removed and allowed to set properly. The cast will turn out accurate and have a smooth outer finish as well. As it is hollow, the cast is definitely much lighter than a solid metal or clay object would be.
Slush casting is usually used to make decorative bowls, vases, lamp bases, candlesticks, miniatures and so on, without the use of cores. The same process is successfully adapted to create a latex mask and other thin skin latex products as well. Cosplay costumes, props and even helmets are made using similar techniques.
Sometimes, closed molds are used for slush casting. The mold is broken apart to reveal a uniquely beautiful cast that cannot be replicated again.
And now that you know how to make molds as well as slush casts, what is stopping you from creating your own hollow ornamental objects?